The present invention pertains to the woodworking industry and, more particularly, to coated cutting tools for cutting articles containing at least a substantial amount of wood.
Steel cutting tools have been used for centuries in the woodworking industry. One reason for the use of steel cutting tools is the ability to form an optimal cutting edge in steel, so that the cut wood has a relatively high quality finish immediately after the cutting. More recently and in an effort to prolong the useful life of cutting tools used in the woodworking industry, steel cutting tools with tungsten carbide tips and cutting tools formed from metal alloys have been used. Additionally, tungsten insert tooling and polycrystalline diamond fused to tungsten carbide substrates have been used. Nonetheless, completely steel cutting tools are often still a very popular choice in the woodworking industry, due, for example, to cost and quality-of-cut considerations.
Additionally, coatings have been applied to cutting tools used in the woodworking industry in an effort to prolong the useful life of the tools. However, such coated tools have had limited commercial success in the woodworking industry, which is indicative of prior coated tools for the woodworking industry failing to sufficiently satisfy the need for economical cutting tools that are capable of making quality cuts throughout relatively long production runs.
In contrast to the woodworking industry, coated cutting tools have been more widely used in the metalworking industry. Examples of coatings used in the metalworking industry are disclosed in U.S. Pat. Nos. 4,992,153 and 5,707,748, both of which are incorporated herein by reference. However, distinctions that exist between the woodworking industry and the metalworking industry are evidence that these industries are nonanalagous fields of art. For example, metal can be many times harder than wood. Additionally, significant variations can exist in a single piece of wood. For example, these variations can be the result of variation in the density of the wood structure, variation in the moisture content of the wood, variation in the interlock and variability of the grain of the wood, hard mineral deposits within the wood, and variations in tension within the wood. Another vast difference in the woodworking and metalworking industries pertains to the use of liquid lubricants/coolants. More specifically, it is conventional to apply liquid lubricant/coolant to a piece of metal that is being cut, but it is typically unacceptable to apply such liquid lubricant/coolant to a piece of wood being cut, because the wood can absorb some of the liquid lubricant/coolant or otherwise be damaged thereby, which can render the wood unacceptable for many uses.
Needless to say, there is always a demand for improved cutting tools for the woodworking industry, with the ideal cutting tool optimally balancing factors such as cutting tool cost, cutting tool longevity, and cut quality. This demand has not previously been fully satisfied For example and as mentioned above, coated cutting tools have found limited commercial success in the woodworking industry. Additionally, many attempts to find a coating for use on cutting tools in the woodworking industry have failed, due to the resulting coated tools providing little, if any, improvement over similar cutting tools without the coating. Accordingly, there is a need for improved coated cutting tools for use in the woodworking industry.
In accordance with one aspect of the present invention, problems are solved by providing a coated cutting tool and using the coated cutting tool to cut a plurality of first workpieces, with each first workpiece being wood or including a substantial amount of wood, to produce a plurality of second workpieces from the first workpieces. More specifically regarding this aspect, the coating is preferably applied via a vacuum procedure to at least a portion of the cutting tool that includes the cutting edge, and the coating preferably includes an inner hard layer and an outer friction-reducing layer over the hard layer. The hard layer is harder than the friction-reducing layer and the friction-reducing layer has a lower coefficient of friction than the hard layer. As a result, the performance of the coated cutting tool advantageously exceeds the performance of a like but uncoated cutting tool.
In accordance with another aspect of the present invention, the coated cutting tool is cryogenically treated to advantageously further enhance its performance In accordance with one aspect of the present invention, the cutting tool is steel, and the coating consists essentially of the hard layer lying directly on the cutting tool and the friction-reducing layer lying directly on the hard layer.
In accordance with one aspect of the present invention, the hard layer includes titanium aluminum nitride, and the friction-reducing layer includes tungsten carbide with carbon.